1. Field of the Invention
The present invention relates to a method and device for calculating an offset direction and a tilt direction of the wire electrode of a wire electro-discharge machining apparatus.
2. Description of the Prior Art
It is known that in the wire electro-discharge machining apparatus, a position of the wire electrode is offset by the dimension thereof so as to perform a precise machining. That is to say, an actual path of the wire electrode (i.e. the centerline of the wire electrode) is located at a position which is shifted by a half of the thickness of the electrode from a theoretical path thereof which coincides with positions of a perimeter of the product to be produced.
Conventionally, a direction of the offset is instructed in a manner such that the actual path of the wire electrode should be on the right or on the left of the theoretical path thereof. For example, as shown in FIG. 1(A), when a product 9 such as a punch tool or the like is inputted and displayed in a numerically controlled product configuration device, an actual path 10 is located at a position shifted on the outside of a theoretical path 11. In this case, if the wire electrode advances during the course of machining operation along the the path 10 in the counter clockwise direction as shown in FIG. 1(A), it is input such that the wire electrode position is shifted on the right of the path 10. Then, the path of the wire electrode or the perimeter of the product is displayed in a display device, for example, as green to distinguish the offset direction.
As shown in FIG. 1(B), when a product 12 such as a die tool is machined, the actual path 13 is located at a position shifted on the inside of the theoretical path 14. In this case, if the wire electrode advances during the course of machining in the clockwise direction as shown in FIG. 1(B), it is input such that the wire electrode position is shifted on the right of the theoretical path 14. The path of the wire electrode is also displayed as green since the offset direction is the same as that shown in FIG. 1(A).
Similarly, as shown in FIG. 3(C) or FIG. 3(D), when the actual paths 15, 17 are located at positions shifted on the outerside of the theoretical path 16 or 18, and the electrode advances during the course of the machining along the paths 16, 18 in the clockwise direction, it is input that the wire electrode positions are shifted on the left of the theoretical paths 16, 18. In this case, the paths 16, 18 are displayed, for example, as yellow to show that the offset direction is different from those of FIGS. 1(A) and 1(B).
In order to machine a taper section in a workpiece, the wire electrode is inclined on the right or the left with respect to the advancing direction thereof. In this case, the direction of the inclination of the wire electrode is input and displayed in the same way as for the above-mentioned wire position offset direction.
However, with this conventional method of input and display of the wire electrode offset direction, when the configuration of the product to be produced is first programmed, and the instruction of the offset direction is input (e.g. this is the case where the configuration is drawn up by a computer aided design system and the like), there is the problem that in order to find the advancing direction of the wire electrode, data sheet and the like, which are used for preparing, the configuration of product, must be checked one by one.
In addition, even in the case where the direction of advancement of the wire electrode is learned from the data sheets and the like, and the instructions for wire offset direction are input as shown in FIGS. 1(A) to (D), there is the further problem that it is difficult to determine intuitively whether the wire electrode offset direction is the direction in which the configuration is contracting or the direction in which the configuration is expanding.
The same type of problem occurs with the direction of the inclination of the wire electrode, which is inclined for machining a taper section in a workpiece, as with the wire electrode offset direction. In particular, whether the configuration is upward-expanding or downward-expending is difficult to determine intuitively.